The present development relates to an absorbent-entrained polymeric structure, having at least one surface and an inner region, wherein the absorbent concentration is greater near the surface than it is in the inner region. Specifically, the migration of the absorbent toward the surface results in the formation of a “layered” structure. The absorbent-entrained polymeric structure may be produced and formed into selected articles by injection molding, blow molding, extrusion or other means of conventional polymer processing.
Many products are most effective and/or aesthetically pleasing when the product is packaged such that the product environment maintains a narrow moisture content range. Although the package environment may be optimal when the product is first packed, maintaining that environment during the lifetime of the product can create many challenges.
For example, many diagnostic test strips and electronic parts are manufactured and packaged so as to minimize the moisture exposure before consumer use. Because the product may be affected by the presence of moisture, the manufacturer must strive to provide a package that will remove any moisture from within the package when the product is first packed, and that will keep moisture out during shipment and display. As is known in the art, additional moisture can be kept out of the package through the use of moisture-impermeable materials. However, moisture-impermeable materials will not affect any ambient moisture that is initially packed with the product—and may actually create more problems by preventing the moisture from exiting from the package. Further, if the package holds product for more than a single use, the consumer's repeated opening and closing of the package will allow moisture to enter the package and will, over time, lead to deterioration of the product.
A different problem is presented when the product itself releases moisture after being packaged. For example, fresh produce can release moisture after being packaged. If the produce is packaged in a non-protective package that allows for moisture permeation, there is a risk that by the time the product reaches the consumer it will have lost too much moisture and will appear “dried out.” However, if the produce is packaged in a moisture-impermeable package that traps the moisture in the package, there is a risk that the moisture will cause the produce to wilt or will allow for bacterial growth within the package. In both situations, the product loses its consumer acceptability.
In order to absorb excess moisture and protect the contained products, absorbing and/or desiccating materials have been introduced into the interior of containers. These absorbents are usually in the form of powders or granules and therefore must be contained in some manner to prevent contamination of the product. The prior art discloses desiccant packed in bags and packets formed from breathable materials, desiccant packed in aerated plastic cartridges, perforated plastic canisters and desiccant tablets. There are problems, however, with using these desiccant-filled containers, such as the risk that the containers could break and release the desiccant freely into the container. There is also the potential for the presence of dust originating from the desiccant and adversely affecting the product to be protected from the moisture. Thus, there is a need for a means of introducing desiccating material into a plastic container or other article of manufacture while somehow preventing the desiccant from releasing and potentially contacting the moisture-sensitive product.
The prior art teaches that desiccant can be entrained into a plastic structure, thereby preventing the desiccant from being released. However, for the desiccant to function as intended, the moisture must be able to make contact with the desiccant. When the desiccant is entrained within the plastic, contact with the moisture is limited. U.S. Pat. No. 5,432,214 (issued Jul. 11, 1995 to Lancesseur) teaches that a fiber can be added to the desiccant-entrained thermoplastic to provide a means for wicking the moisture into the interior of the polymer and to the desiccant. However, the selection of fibers for a '214 polymer is limited because few fibers have been approved by the Food and Drug Administration for use in pharmaceutical packaging and because the fibers must be able to withstand the extrusion process. Alternatively, U.S. Pat. No. 5,911,937 (issued on Jun. 15, 1999 to Hekal) teaches the use of channels that are created with a channeling agent. The channeling agent “form[s] passages in the mixture through which moisture is communicable to desiccating agent that is entrained within the mixture.” However, preparing the '937 polymer can be challenging. As noted in the '937 patent “because of the relatively fine size of the desiccant particles, it is advantageous to have many small channels or passages throughout the polymer base, as opposed to a few large channels that will expose less surface area within the polymer solid.” To accomplish this, polymer additives may be needed.
The desiccant is most accessible, and there is a greater probability that the moisture can make contact with the desiccant, if it is entrained near the surface of the plastic. In U.S. Pat. No. 4,665,050 (issued May 12, 1987 to Degen et al.), heated absorbent particles are secured onto a thermoplastic material such as polyethylene or polypropylene, preferably such that each sorbent particle is not completely enveloped in the polymeric binding material but rather that each particle merely be held in place by the polymeric binding material. While the resulting polymer has good adsorbent accessibility, the process to form the polymer is tedious.
It is accordingly a primary object of the invention to provide an absorbent-entrained polymeric composition that will provide for an effective amount of moisture-to-absorbent contact without the use of fibers or hydrophilic compounds that might contaminate a moisture sensitive product coming in contact with the polymeric composition. It is a further object of the invention that the absorbent-entrained polymeric composition be relatively easy to prepare or manufacture.